Description of the Related Arts
It is well known in the art that the roving of roving bobbins suspended by bobbin hangers on a creel of a ring spinning frame is provided with a low twist, and thus the tensile strength of such a roving is very weak, and therefore, the roving is easily broken under a low tension. Accordingly, the operation of piecing rovings at the time of a roving bobbin exchange operation have been manually carried out. To apply an automatic operation system to this roving bobbin piecing operation, the method of exchanging roving bobbins in the spinning machine and the apparatus for carrying out this method were developed by the present inventors, and these new developments were disclosed in Japanese Unexamined Patent Publication Nos. 62 (1987)-53426 and 62 (1987)-53425, respectively. In these new developments, a plurality of almost exhausted or exhausted roving bobbins (six roving bobbins in the embodiment) in the front row on the creel are changed for a plurality of full packaged roving bobbins (six full packaged roving bobbins in the embodiment) reserved on a supply rail, and the respective rovings of the exhausted or almost exhausted roving bobbins and the respective rovings of the corresponding full packaged roving bobbins are pieced when exchanging the roving bobbins. The above mentioned roving bobbins in the exhausted or almost exhausted condition are hereinafter referred as the exhausted roving bobbin. However, these inventions have a problem in practical application in that the inventions are applicable only to a spinning frame equipped with a roving bobbin interchanging device, because the full packaged roving bobbins which have replaced the exhausted roving bobbins in the front row of the creel and full packaged roving bobbins in the back row of the creel must be interchanged before the next roving bobbin exchanging operation.
To solve this problem, methods of simultaneously exchanging a pair of front and back exhausted roving bobbins for two adjacent full packaged roving bobbins reserved on a supply rail are proposed, for example, in Japanese Unexamined Patent Publication Nos. 61 (1986)-119728 and 61(1986)-102428. However, the function of either method is limited to merely automating the work for exchanging exhausted roving bobbins for full packaged roving bobbins respectively. Furthermore, according to those methods, four pegs, i.e., two pegs for exhausted roving bobbins and two pegs for full packaged roving bobbins, are moved along separate three-dimensional paths, respectively, when exchanging the roving bobbins, and thus those methods require a large space for carrying out the roving bobbin exchanging operation, and the roving bobbin exchanging device has complicated construction. Accordingly, it is difficult, from the view-point of design, to incorporate mechanisms necessary for piecing rovings into such a roving bobbin exchanging device. Simultaneous execution of a unit roving piecing operation and roving bobbin exchanging operation applied for two roving bobbins, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 62-6298, of the present inventors, requires a long time, i.e., at least three times the time required for carrying out the roving bobbin exchanging operation/spindle by the invention disclosed in Japanese Unexamined Patent Publication No. 62 (1987)-6298, and therefore, this invention is practically undesirable because of the very long time necessary for exchanging all of the roving bobbins on the creel of such a spinning frame having two hundred and forty spindles or above on one side thereof.